1. Field of the Invention
The present invention relates generally to optical switches of the integrated optic type, and more particularly to a liquid crystal based thermo-optic switch capable of redirecting optical beams of arbitrary polarization state in a channel waveguide geometry. Additionally, the invention relates to an integrated optic variable attenuator based on this switch architecture.
2. Description of the Related Art
Currently, a typical integrated optic switch employs either electro-optic [see for example R. C. Alferness, “Guided Wave Devices for Optical Communication”, IEEE J. Quantum Electron., vol. QE-17, pp. 946–958 (1981); U.S. Pat. Nos. 4,070,092 and 4,775,207] or thermo-optic [see for example B. A. Moller, L. Jensen, C. Laurent-Lund, and C. Thirstrup, “Silica Waveguide Thermo-Optic Phase Shifter with Low Power Consumption and Low Lateral Heat Diffusion”, IEEE Photonics Technol. Lett., vol. 5, pp. 1415–1418 (1993); U.S. Pat. Nos. 6,084,050 and 6,311,004] effects to produce differential refractive index loading between two optical pathways within the switch which in turn directs the guided optical mode into a particular output pathway, usually the higher loaded pathway. The refractive index loading produced by electro-optic effects is inherently birefringent in that these materials load the two polarization states of the guided mode(s) differently which complicates the switch design. Thermo-optic loading can be polarization independent but the magnitude of the effect in currently available thermo-optic materials is limited requiring high differential temperatures to induce complete switching. Liquid crystal based optical switches [see for example R. A. Soref, “Liquid-Crystal Fiber-Optic Switch”, Opt. Lett., vol. 4, pp. 155–157 (1979); M. Kobayashi et al., “2×2 Optical Waveguide Matrix Switch Using Nematic Liquid Crystal”, IEEE J. Quantum Electron., vol. QE-18, pp. 1603–1610 (1982); U.S. Pat. No. 4,828,362] benefit from the large refractive index loading provided by the liquid crystal reorientation but are also sensitive to the polarization state of the optical radiation being switched. Due to these limitations, current integrated optic switches can be difficult to implement.